Two terms you must become familiar with overnight are “Safety-Related” and “Class 1E.” In this post I focus on safety-related . . . .
The NRC is most focused on preserving the health and safety of the public. It labels “safety related” any system, structure, or component which is critical to doing that. This term is meant to focus our attention on the gravity of our responsibilities when developing mods and replacing equipment. Whenever any aspect of a modification interacts with any safety-related SSC, plant procedures automatically call down the most intense levels of rigor and scrutiny because of the importance that the NRC has placed on them.
Safety-related systems, structures, and components have three characteristics. They ensure:
- the integrity of the reactor coolant pressure boundary (the reactor vessel and associated piping that circulates the reactor coolant);
- the capability to shut down the reactor and maintain it in a safe shutdown condition; or
- the capability to prevent or mitigate the consequences of accidents that could result in potential offsite exposures
A containment isolation valve is safety-related, for example, because by isolating the reactor coolant lines it confines radioactivity to the containment building and performs the functions defined above. It helps keep radioactivity away from the public.
An emergency diesel generator is safety-related because, by providing backup power to safety-related equipment, it ensures the capability to shut down the reactor and maintain it there safely. Again, Fukushima was so disastrous because without the emergency diesel generators to operate safety-related equipment (like pumps), the reactors were incapable of being maintained in a safe shutdown condition. The coolant wasn’t able to continue circulating through the reactor to keep it cool following the SCRAM.